1. Field of the Invention
The present invention relates generally to a magnetic tape cartridge for use as a data storage media. More specifically, the invention relates to a magnetic tape cartridge compatible with a disk drive and being particularly useful as backup storage media for a computer. Further particularly, the invention relates to a tape drive mechanism for a disk-drive-compatible magnetic tape cartridge, in which the tape drive mechanism is capable of steadily driving the magnetic tape both in forward and reverse directions.
2. Description of the Background Art
As is well known, magnetic tape has a relatively large data storage capacity. Magnetic tape is especially useful as a storage medium when fast access is not required, such as when used for backup storage. However, on the other hand, because of the relatively slow access to the desired data, tape is less popular than disk-type storage media, such as floppy disks, hard disks and so forth. Therefore, recent computers generally employ disk-based data storage systems as built-in or external units.
Various floppy disks and disk drives designed for use with associated disks have been developed and proposed. For example, the U.S. Pat. No. 4,445,155, issued on Apr. 24, 1984, to Takahashi et al discloses a typical construction of a microfloppy disk, i.e. a 3.5-inch floppy disk and a disk drive therefor. The floppy disk is in the form of a floppy disk cassette or cartridge generally comprising a flexible magnetic disk and a cassette or cartridge casing. The flexible disk includes a center core disk designed to be chucked on a turntable of the disk drive. The disk drive drives the flexible disk and the center core disk to rotate.
Floppy disks are useful for fast access. On the other hand, floppy disks have limited data storage capacity. Archival or backup storage of data stored on a hard disk generally takes 20 to 80 floppy disks due to the larger capacity of a hard disk. This involves substantial expense to the user. On the other hand, magnetic tape can easily accommodate all of the data stored on a hard disk, as is well known. However, a special tape recording and/or reproducing apparatus has previously been necessary for copying data from the hard disk onto the magnetic tape storage medium. This is an additional expense for the user.
So as to allow the user to utilize magnetic tape for inexpensive backup storage of data on hard disks or floppy disks, it would be beneficial to provide a magnetic tape cartridge compatible with floppy disk drives so that it may be driven by the same drive unit as floppy disks.
Generally, the magnetic disk, the usual media to be used with the disk drive, is driven in rotating fashion. Therefore, one-way driving to drive the disk in a fixed single direction will never raise any significant problem. However, on the other hand, in case of the disk-drive-compatible magnetic tape cartridge, a difficulty is encountered in the single direction driving. Namely, as long as only single direction, i.e. forward direction, driving is allowed for the disk drive, the access period for accessing over various recording tracks on the magnetic tape becomes unacceptably long, since such single directional driving requires a rewinding operation to switch recording tracks to be accessed. Therefore, it is preferable to provide two-way driving, i.e. forward and reverse direction drive, of the magnetic tape.
However, since the normal disk drive systems have been designed to drive the magnetic disk in a single direction, reverse direction driving has been impossible due to slip caused between the turntable of the disk drive and the center core disk of the magnetic tape cartridge and resulting in misalignment of tape information tracks in relation to the magnetic recording head of the disc drive.